Phasing of multisection linear accelerators by alternately turning on and off appropriate electromagnetic drivers



G. A. LOEW June 21, 1966 PHASING OF MULTISEGTION LINEAR ACCELERATORS BY ALTERNATELY TURNING ON AND OFF APPROPRIATE ELECTROMAGNETIC DRIVERS 2 Sheets-Sheet 1 Filed March 18, 1965 w E R10. O mA E VY R m0 G oSmE@ E@ OCME@ M G a ,wm/V en vm mv @@2152 5232 6252 6239 5232 5252 V.. u k B mm mm Nm ci@ ov m\ S 51:58 o. 5.526 3 mno@ o, bmx ivm mw; @NL EN T :I :I mm 5K5@ mw m21@ m21@ w21@ :NNI mw 7 NNL TA L E T@ LVFM N1 Q m1 E r ATTORNEY June 21, 1966 G. A. LOEW 3,257,577

PHASING OF' MULTISECTION LINEAR ACCELERATORS BY ALTERNATELY TURNING ON AND OFF APPROPRIATE ELECTROMAGNETIC DRIVERS Filed March 18, 1965 1 Sheets-Sheet 2 COUP-LER ATTORNEY United States Patent O 3,257,577 PHASHNG F MULTISECTION LINEAR ACCEL- ERATORS EY ALTERNA'EELY TURNING 0N AND @FF APPRPRHATE ELECTROMAGNETIC DRHVERS Gregory A. Loew, Palo Atto, Calif., assigner to the United States of America as represented by the United States Atomic Energy Commission Filed Mar. 18, 1963, Ser. No. 266,117 8 Claims. (Cl. S15-3.6)

This invention relates to the phasing of multisection linear accelerators, and is particularly directed to .a relatively simple method and apparatus for phasing the individual microwave tubes which supply driving energy to a multisection elec-tron linear accelerator, in proper relationship to maximize the energy of the electron beam as it passes through the successive sections of the accelerator.

Various phasing methods have been devised to phase the microwave driving sources supplying electromagnetic energy to the respective waveguide sections of an electron linear .accelerator for maximum energy of the output beam. More particularly, the driving source associated with each section must be phased to lobtain maximum energy transfer to the electron beam as it passes through that section. In accordance with some previous methods, the proper phase relationship may be established by suitably phasing the driving electromagnetic energy in a section with respect to the phase of the beam in that section, section-by-section, along the entire length of the accelerator. Phasing methods of this type, which depend on interaction between the beam and the driving energy in the detection of the phase therebetween, require the presence of a substantial beam during the complete phasing operation. In an accelerator formed of a large number of accelerating sections such a beam is often not available in all sections at `the time of the phasing operation, or the beam current may be too low in some sections to facilitate the necessary sensitivity. Various other methods for phasing a multisection accelerator have involved Ithe establishmentof the proper phase relationship between the driving energy `and beam in one section, and the use of this adjusted phase tof the driving energy as a reference to which the phase of the driving energy in successive sections :may be compared and correspondingly adjusted. Methods of the latter comparison Variety sulfer from the difficulties encountered in establishing length equality of the respective waveguides or transmission lines, which are utilized to couple the microwave driving tubes associated with adjacent sections to a phase detector for indicating the phase rela-tionship between the driving energies supplied to the respective sections. Unless the microwave path lengths to the phase detector are identical, the phase relationship indicated by the detector could possibly be in error.

In accordance with the present invention an improved phasing method is provided wherein advantages of the foregoing previous types of phasing methods are combined, while their respective disadvantages are eliminated. In addition, atypical apparatus .arrangement of relatively simple form is provided for conducting the phasing method, while alternative arrangements for conducting the phasing method are also developed.

Accordingly, it is an object of the present invention to provide method and apparatus for phasing a multisection particle linear accelerator without requirement of the presence of a substantial beam in allsect-ions of the accelerator, nor absolute equality between microwave path lengths over which signals from respective sections are transmitted to a detector for phase comparison.

It is another object of the present invention to provide a method and apparatus for phasing a multisection wave- Patented June 2l, 1966 ice gu-ide linear accelerator which accelerates either a positive or negative charged particle beam.

Another object of the invention is to provide a multisection linear accelerator phasing method wherein the signals derived for phase comparison are inherently of comparable magnitudes.

It is yet another object of the invention to provide a phasing method of the class described which allows continuous monitoring of the phase of the klystron tubes without the presence of high beam current; high beam current being needed only periodically (e.g., once a week) to establish a reference minimum with beam induced radio frequency signals.

Still another object of the invention is to provide a phasing method of the class described wherein gating of the signals extracted for .phase comparison is not required.

It is yet another object of the invention to provide a phas-ing method of the class described which may be carried out with a relatively simple apparatus arrangement wherein equipment requirements are minimal.

lt is still another object of the present invention to provide a phasing method of the class described wherein the section output signals to be used for phasing the klystrons are brought to a central point and are individually compared in random sequence to the phase of any single reference klystron. f

A furtherobject of the present invention is to provide a .phasing method of the class described wherein phasing lof a plurality of klystrons wherein one or several of the klystrons are inoperative is read-ily accomplished with no change in the existing phasing circuitry.

Yet a further object of the invention is to provide method and `apparatus of the class described which .are readily adapted to automation.

Additional objects and advantages of the invention will -become apparent from the following description and claims considered together with the accompanying drawing, of which:

'FIGURE l is a schematic diagram of typical apparatus as employed in conjunction with a multisection electron linear accelerator to facilitate phasing thereof in accordance with the present invention.

'FIGURE 2 is a schematic diag-ram of -an alternative embodiment of the apparatus of FIGURE l, and

FIGURE 3 is a partial schematic of .a modied ernbodiment of the apparatus of FIG. 2.

Referring now to FIGURE l a portion of a multisection traveling-wave linear electron accelerator is designated at 10. It is to be understood that although the invention is herein described in conjunction with a linear traveling-wave electron accelerator, such method and apparatus is adaptable for use in phasing other accelerators, such as, for example, a linear traveling-wave proton accelerator. The electron accelerator ll() is of generally conventional construction and includes a plurality of loaded waveguide sections i2 coaxially aligned end-toend; the loading being provided by a plurality of disks 13 disposed therealong. An electron gun lili or other suitable source of electrons is provided at the input end of the accelerator to introduce a hunched electron beam axially into the first waveguide section. Each of the sections l2 is driven at its input end by a klystron 16, 16 and I6 or equivalent microwave power ampliiier tube, which klystron is coupled to its corresponding section. The klystrons 16, 16l and 16" are driven by a master oscillator 1S which feeds a pulsed drive line coupled to the klystrons through corresponding klystron phase Shifters 22, 22 and 22". The output end of each waveguide section is coupled to a load 24, 24', 24" through corresponding directional couplers 26, 26 and 26". Thus, the klystrons propagate traveling electromagnetic waves through their respective waveguide sections 12. At such time as these waves are in proper phase relative to each other and to an electron beam introduced into the first section from electron gun 14, the beam is accelerated through the successive sections with a maximum transfer of wave energy from the klystrons to the beam. The klystron phase shifters 22, 22', 22 facilitate adjustment of the corresponding klystrons 16, 16 and 16 to set the phases of the waves in the respective sections in varied relationships to each other, and to the beam.

Referring now in particular to the center section of the FIGURE 1, a coaxial cable 28 couples the output of directional coupler 26 to a corresponding magic T 30 through an isolator 32 and simple T junction 34. The remaining arm of the simple T junction 34 is coupled through an isolator 36 to a successive magic T 38 of the adjacent accelerator section. One of the remaining ports of the magic T 30 is coupled to a circuit identical to that described, supra comprising in particular, an isolator 40, a simple T junction 42, coaxial cable 44 and the directional coupler 26'. The other two ports of the magic T 30 are coupled respectively to a movable short-circuiting plunger 48, and a detector means 50 comprising for example, a crystal detector with a suitable indicator such as a cathode ray oscilloscope or a voltmeter (not shown). The combination of the magic T 30, and detector means 50 is designated herein as a phase detecting means 52.

To reiterate, only three accelerator sections 12 including respective klystrons, phase shifters and associated phasing circuits, are shown to exemplify the mechanism of the invention. The phasing circuits as previously described, are each coupled to an output of the sections 1.2 and comprise, as an example, a directional coupler 26 located ahead of the load 24. A signal is thereby coupled from the output of the corresponding section, and is transmitted along a suitable length of liexible coaxial cable 28 and divided by means of the simple T junction 34. The length of the cable 28, as well as cable 44, is preferably equal to the shortest practical distance from the section output to the T junction 34. Thus, two signals are available from consecutive, simple T junctions (eg, 34 and 42) and are fed into the magic T 30 through isolators 32 and 40. The isolators are employed in the embodiment of FIGURE 1, in order to isolate signals from nonadjacent accelerator sections, while permitting the comparison of the signals from adjacent sections. In most applications of the described apparatus, the magic T 30 is in general best placed approximately midway between two adjacent accelerator sections, particularly when extremely precise phasing is desirous and the long line effect could comprise a source of error.

The phasing method in accordance with the invention is conducted utilizing the foregoing structural arrangement. At such time as the beam is available in two consecutive sections, the corresponding two klystrons, for example, klystron 16 and 16', are turned off and the movable short-circuiting plunger 48 disposed in the magic T 30 is moved until the output power from the output arm goes through a minimum, as indicated by the detector means 50. This is, the magic T `short-circuiting plunger 48 is adjusted to show a null reading in the detector means 50. This adjustment action determines the minimum value of signal difference between thev beam-induced signals arriving from the two accelerator section outputs, and more particularly, the two directional couplers 26, 26', and provides thus a reference null for subsequently comparing and adjusting the phase of the adjacent klystrons 16, 16. Provided that the coaxial cables are not disturbed or stretched, the minimum, or reference null, obtained should remain at this point for a reasonably long period of time, and has to be determined only periodically.

With the two klystrons 16, 16 on, the phase shifter 22 and thus the compared phase of the klystron 16, is sub` sequently adjusted to again provide a minimum signal reading, or null, as indicated and observable on the detector means 50 disposed in the arm of the magic T 30. It is CTl ' manner well known in the art.

all subsequent, adjacent klystrons within a sector, thus insuring that they are all beam phase coherent with the irst klystron of the sector. That is, within the period of time that the reference null remains the same, and while the accelerator is operating, or while all the klystrons are on and phasing is desired, starting at the beginning of a sector, consecutive phase shifters are tuned or` .adjusted until the power out of each common magic T again goes through a null. In other words, the phase of the klystron-generated wave is adjusted by the corresponding phase shifter until the phase of the resultant wave at the output end of the respective section bears a 180 relationship to the phase of the beam-induced wave passing therealong.

With the typical apparatus arrangement hereinbefore described, the tuning of each phase shifter, or klystron, is preferably done in the consecutive sequence because each klystron within the sector determines the phase of the successive klystron. That is, assuming klystron 16 is the first in the sector, then klystron 16 is phased with klystron 16', klystron 16 with klystron 16, the next klystron (not shown) with klystron 16", etc.

Actually, the radio frequency instrumentation (or phasing circuitry) shown beyond the directional couplers (26, 26, 26") is only typical for the apparatus hereinbefore described, Vand is by no means unique. It is also possible, for example, to eliminate all isolators and all but one magic T of the FIGURE 1 embodiment of the invention, and to bring all signals from the couplers to one central point. Notice that the function of the magic T (30) with a movable short-circuiting plunger (48) is `simply to combine the functions of a T and a reference phase shifter. By means of a rotary radio frequency switch located at said central point it is possible to compare the phase of any given klystron to that of any other klystron. Thus, the cumulative errors that can arise by sequentially phasing the klystrons as provided by the phasing apparatus shown in FIGURE 1, may be circumvented by utilizing the alternative apparatus.

The alternative apparatus employs the phasing method in accordance with the present invention, and may -be further understood by referring to FIGURE 2, which exemplifies a portion of a multisection traveling-wave linear electron accelerator 10 comprising in part, sections l12, an electron gun 14, and klystrons 54, 56, 58 with respective klystron phase shifters 60, 62, 64; the combination of phase shifter and klystron being connected to the input end of respective sections 12, whereby electromagnetic energy is introduced to each section in a For example, the principles of operation of the electromagnetic linear accelerator, including the manner of introducing radio frequency driving energy thereto, are fully explained in the publication Review of Scientific Instruments, vol. 26, No. 2, pp. 134-209, and therefore are not further discussed herein. Loads 66, 68 and 70 are coupled to the output end of corresponding sections 12 of the accelerator. Signals are extracted from directional couplers 72, 74 and are transmitted along respective tiexible-coaxial cables 78, and are extracted from directional coupler 76 and transmitted to Calibrating phase shifters 84, 86, and 88 respectively. The Calibrating phase shifter 84 is coupled in turn to a phase detecting means 90 which comprises the combination of a magic T 92 and a detector means 94 of the type previously described in FIGURE l. The common side of a rotary switch 96 or equivalent switching device is coupled to the port of the magic T 92 opposite the port connected to phase shifter 84, and the various contacts of the switch 96 are connected to Calibrating phase shifters 86 and 88 as well as calibratng phase shifters 98, 100, etc.; the latter phase shifters being connected to other sections 12 (not shown) of the accelerator by coaxial cables 102, 104, similar to cables 78, 80 and 82. The number of coaxial cables and calibrating phase shifters, as well as the number of contacts on the rotary switch 96 is determined by the number of sections, and corresponding klystrons, being phased. In utilizing the alternative apparatus of the invention, the practical number of klystrons or sections which are .preferably phased with one phase detector means 90, depends generally on the permissible and practical lengths of the coaxial cables, and various economic factors such as the cost of the detector means, magic Ts, etc.

The operation of the alternative apparatus for phasing a group or sector of klystrons or sections, corresponds to that described in 4conjunction with the apparatus of FIGURE 1, except that there is no need to .phase the klystrons consecutively. For example, it is not necessary to determine the phase of klystron 56 by comparing it with the phase of klystron 54, and then klystron S8 with klystron 56, etc. Rather, any of the klystrons of the sections grouped together to form a sector can be selected at random for phasing, thus circumventing any cumulative errors which may arise and allowing phasing to take place even if one or several klystrons of the group or sector happen to be out of operation.

More particularly, in phasing the klystrons with the alternative apparatus of FIGURE 2, `at such time as the beam is available, klystron S4 and, for example, klystron 58 are turned off and the rotary switch 96 i-s set to the contact 106 corresponding to the section into which klystron 58 introduces energy. Then the calibrating phase shifter 8S is adjusted until the output power from the magic T 92 goes through a minimum value as observed on the attached detector means 94. Next, the two klystrons 54 and 58 are turne-d on, and the corresponding klystron phase shifter 64 is adjusted to again provide a minimum signal reading, or null, as observed on the detector means 94.

It will be appreciated that the terms observe and determine7 as employed herein with respect to the present method of observing or determining phase, are understood to include various comparison techniques, such as setting two reference phases equal by null detection, and comparing the phase of two signals to that of the reference by null detection. The terms thus, are inclusive of techniques which teach the existence of a predetermined phase relationship.

This sequence of operations is thereafter repeated for all klystrons in the sector; that is, all klystrons therein are phased against the one klystron 5'4, thus insuring that all the klystrons are beam phase coherent with one klystron. Since the phase of successive klystrons is not dependent upon the phase of preceding klystrons, there is no possibility of there occurring cumulative phase errors.

FIGURE 3 shows a modified apparatus of the apparatus of FIG-URE 2, wherein the single rotary switch 96 is replaced by two rotary switches 106 and 10S. Calibrating phase Shifters 110 are disposed in each incoming v coaxial cable. The common side of the rotary switches 106, 108 are in turn connected to opposite ports of a magic T 114 through respective isolators 1,16. The magic T 1-14 is coupled at one port to a detector means which comprises a detector crystal 118 and a cathode ray oscilloscope 120 and/or a suitable voltmeter 122.

In utilizing the modified embodiment shown in FIG- URE 3 there is no preferred sequence for selection of the phasing operations; that is, the sections and klystrons to be phased are again selected at random. Howe-ver, due to the use of the two rotary switches, it is possible to shift from the rst reference klystron (as described in conjunction with FIGURE 2) to a second reference klystron, if the rst fails for any reason. Thus, the modified embodiment of FIGURE 3 is a more versatile achieved for the entire accelerator.

6 version of the alternative embodiment of FIGURE 2. In both the embodiments phasing can be conducted on the entire accelerator even though one, or several, kly- 4strons are inoperative, with no need for bypassing the klystron with cables, or otherwise disturbing the phasing circuitry with additional temporary components.

The embodiments of FIGURES 2 and 3 likewise can be relatively simply adapted to automation. That is, the phasing circuitry, or more particularly the phase detecting means circuitry, can be replaced for example, with an automatic system which includes a gated voltmeter, a programmer to automatically perform sequential phasing of all sections in a sector, a servo-amplifier to seek the minimum seen in the magic T, a phase wobbler capable of modulating the phase by i around the phase set by the Calibrating and klystron phase Shifters, and a divide-by-two network which permits readout alternately of -land 90 around the phase set by the system. When a minimum is attained, the gated voltmeter yields equal outputs that correspond to a Zero output for the servo-amplier.

Likewise, the electronic detector means could be constructed as a portable package, which could be moved as desired to the central points of previous mention (FIGURES 2 and 3), and plugged into available connectors on the microwave components of the phasing apparatus. Thus, a single electronic detector means could be utilized to phase the entire accelerator.

It is to be understood that to turn off a klystron such as when determining the beam-induced minimum signal reference, it is not necessary to actually remove the power from the klystron. For phasing purposes, the klystron in essence can be turned off simply by triggering it late, so that the beam-induced signal can be readily distinguished from the klystron produced wave signal as observed in the oscilloscope. It is preferable in some instances to trigger the klystron late rather than remove entirely the power fed thereto, because such manner of operation' provides a more constant heat dissipation and thus constant frequency conditions, of the various power delivering components, for example the klystrons, waveguides and accelerator sections.

After so phasing together the individual sections within each separate sector, the phasing of such sectors with one another, thus completing the phasing of the entire accelerator, can be effected by applicants hereinbefore disclosed method in like fashion, in preference to any previously conventional techniques such as, for example, the energy maximization technique. Consequently, the techniques described herein enable phase coherence to be achieved between all klystrons. However, in order to establish phase coherence between the beam passing through the accelerator and all klystrons in the accelerator structure, the radio frequency energy going to the buncher section of the accelerator may be phased separately until a maximum energy-out condition is Alternately, there are various known methods for comparing and adjusting, the phase of the first klystron and the phase of the beam, as for example, by means of the method disclosed in a copending application of David J. Goerz, Ir., et al., Serial No. 182,691.

It is to be understood that the various phasing components, e.g., directional couplers, simple and magic T junctions, phase Shifters, phase detecting means, etc., as well as their inherent functions, are well known in the art and particularly explained in the publication The International Dictionary of Physics and Electronics, D. Van Nostrand Co., Inc., Princeton, New Jersey, 1956.

Thus while the invention has been disclosed with respect to several embodiments, it will be apparent to those skilled in the art that numerous variations and modifications may be lmade within the spirit and scope of the invention and it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

1. In a method for phasing a section of a multisection linear charged particle accelerator wherein a charged particle beam is accelerated by means of a driving electromagnetic wave the steps comprising adjusting the phase of a beam induced output signal of said section relative to the phase of a beam induced output signal of a reference section in the presence of said charged particle beam passing therethrough and in the absence of said driving electromagnetic wave to obtain a minimum value of signal difference between the beam in-I duced output signals, and adjusting the phase of the driving electromagnetic wave of said section in the presence of said charged particle beam and said driving electromagnetic wave passing through the sections to realize a minimum value of signal difference between an output signal of said section and an output signal f said reference section.

2. A method for phasing the respective sections of a multisection linear accelerator wherein a charged particle beam is accelerated through successive sections by imposition of driving electromagnetic waves established therein by a plurality of klystrons respectively coupled to the input end of the section comprising the steps of,

(a) introducing said charged particle beam to at least two of said succession of sections to generate a beam induced signal therein,

(b) introducing to a common point said beam induced output signal from said ltwo sections,

(c) adjusting the phases of the beam induced signals at said common point to obtain a minimum value of signal difference therebetween,

(d) establishing said driving electromagnetic waves within said two sections by means of said klystrons,

(e) introducing to said common point an output signal extracted from said two sections in the presence of said driving electromagnetic waves and said charged particle beam, and

(i) adjusting the relativeV phase of the driving electromagnetic waves of said sections to obtain a minimum value of signal difference between the output signals extracted in the presence of said driving electromagnetic waves.

3. The method in accordance with claim 2 wherein the sequence of steps is repeated on pairs of said sections within said succession of sections.

4. The method in accordance with claim 2 wherein the sequence of steps is repeated on each successive section and associated klystron with respect to the preceding phased section and klystron.

5. A method for phasing a multisection electron linear accelerator wherein an electron beam is accelerated 4through successive sections by driving electromagnetic waves established therein by a plurality of klystrons respectively coupled to the input ends of the sections comprising the steps of,

(a) turning ot two klystrons of corresponding sections of said succession of sections,

(b) extracting a beam induced signal from the output ends of said corresponding sections in the absence of said driving electromagnetic Waves,

(c) introducing said extracted beam induced signals to a common point,

(d) adjusting the phases of the beam induced signals at said common point to obtain a minimum value of signals difference therebetween,

(e) turning on said two klystrons to produce said driving electromagnetic Waves within said corresponding sections,

(f) extracting an output signal from said corresponding sections in the presence of said driving electromagnetic waves and said charged particle beam,

g) introducing said output signals extracted from said corresponding sections in the presence of said electromagnetic waves and said charged particle beam to said common point,

(h) adjusting the relative phase of the driving electromagnetic waves of said sections to obtain a minimum value of signal difference between the extracted output signals at said common point, and

(i) repeating the sequence of the steps (a) through (h) on pairs of sections and associated klystrons within said succession of sections.

6. The method in accordance with claim 5 wherein the sequence of steps is repeated on each successive klystron and associated section with respect to the preceding phased klystron and section..

7. A method for phasing the respective sections of a multisection linear accelerator wherein a charged particle beam is accelerated through successive sections by driving electromagnetic waves established therein by plurality of klystrons effectively coupled tothe input end of the section comprising the steps of,

(a) turning off two klystrons of corresponding sections of said succession of sections,

(b) establishing said charged particle beam within said corresponding sections to generate a beam induced signal therein,

(c) introducing said beam induced output signals to a phase comparing means,

(d) adjusting the phases of the beam induced signals by means of a rst phase shifting means to obtain a minimum value of signal difference therebetween as indicated by said phase comparing means,

(e) `turning on said klystrons to establish the driving electromagnetic waves within said corresponding sections,

(f) extracting an output signal from said corresponding sections in the presence of said beam and said driving electromagnetic waves,

(g) introducing said output signals to said phase comparing means, and adjusting the relative phase of said two klystrons to obtain a minimum value of signal difference between said extracted output signals as indicated by said phase comparing means.

8. A method for phasing a multisection electron linear accelerator wherein an electron beam is accelerated through successive sections by driving electromagnetic Waves established therein by a plurality of klystrons respectively coupled to the input ends of the sections comprising the steps of,

(a) turning off two adjacent klystrons of corresponding adjacent sections of said succession of sections,

(b) comparing with al phase detecting means the phases of beams induced waves extracted from the output ends of said adjacent sections in the absence of said driving electromagnetic waves,

(c) I tuning the phases of the compared beam induced waves to obtain a minimum value of signal difference therebetween, v

(d) turning on the adjacent klystrons to produce said driving electromagnetic waves within said adjacent sections,

(e) comparing with a phase detecting means the phase of the signals extracted from the output ends of said adjacent sections in the presence of said beam and said driving electromagnetic waves,

(f) tuning the relative phase of said klystrons to obtain a minimum Value of signal difference between said extracted output signals as indicated by said phase detecting means, and

(g) repeating the sequence of steps (a) through (f) on pairs of sections within said succession of sections.

References Cited by the Examiner UNITED STATES PATENTS 3,147,396 9/1964 Goerz et al 3l5-5.42

HERMAN KARL SAALBACH, Primary Exrminer.

R. D.v COHEN, Assistant Examiner. 

1. IN A METHOD FOR PHASING A SECTION OF A MULTISECTION LINEAR CHARGED PARTICLE ACCELERATOR WHEREIN A CHARGED PARTICLE BEAM IS ACCELERATED BY MEANS OF A DRIVING ELECTROMAGNETIC WAVE THE STEPS COMPRISING ADJUSTING THE PHASE OF A BEAM INDUCED OUTPUT SIGNAL OF SAID SECTION RELATIVE TO THE PHASE OF A BEAM INDUCED OUTPUT SIGNAL OF A REFERENCE SECTION IN THE PRESENCE OF SAID CHARGED PARTICLE BEAM PASSING THERETHROUGH AND IN THE ABSENCE OF SAID DRIVING ELECTROMAGNETIC WAVE TO OBTAIN A MINIMUM VALUE OF SIGNAL DIFFERENCE BETWEEN THE BEAM INDUCED OUTPUT SIGNALS, AND ADJUSTING THE PHASE OF THE DRIVING ELECTROMAGNETIC WAVE OF SAID SECTION IN THE PRESENCE OF SAID CHARGED PARTICLE BEAM AND IN DRIVING ELECTROMAGNETIC WAVE PASSING THROUGH THE SECTIONS TO REALIZE A MINIMUM VALUE OF SIGNAL DIFFERENCE BETWEEN AN OUTPUT SIGNAL OF SAID SECTION AND AN OUTPUT SIGNAL OF SAID REFERENCE SECTION. 